Devices for automatically measuring blood pressure have become increasingly more popular. These devices typically allow a user to obtain quick blood pressure measurements without requiring a stethoscope or medical personnel. Further, due to the automated nature of these devices, the user does not need to participate in making the measurement except to put a conventional blood pressure cuff to his arm and start the measurement.
Most automated blood pressure measuring devices currently available rely upon a processor controlled pneumatic system to increase the pressure of the cuff enough to occlude the brachial artery. Once the cuff has attained a pressure sufficient to substantially occlude the brachial artery, the processor controlled pneumatic system slowly decreases the pressure of the cuff, either continuously or in increments. As the pressure of the cuff is reduced, the processor controlled pneumatic system records the pressure of the cuff at regular increments.
When the pressure in the cuff is reduced to systolic pressure, the flow of blood through the brachial artery beneath the cuff increases substantially. Following each contraction of the heart, blood flows through the brachial artery imparting pulsatile movement to the wall of the artery. This pulsatile movement causes minute changes in the pressure of the cuff, which changes are known as oscillometric pulses, and are recorded by the automatic blood pressure measuring device. As the pressure in the cuff is reduced toward zero, a table is created that contains values for the oscillometric pulse amplitude recorded at each cuff pressure. By processing the oscillometric pulses recorded in the table, the automatic blood pressure measuring device can determine relatively accurately the user's blood pressure.
Since these automatic blood pressure measuring devices are provided for substantially hands-free operation by unskilled users, it is necessary that they be constructed to operate properly with little or no maintenance. However, after prolonged use, dust, dirt, and other debris may collect in the pneumatic system of the device. This debris tends to clog the valves, and other devices of the pneumatic system, and substantially detract from proper operation of the automatic blood pressure measuring device. Accordingly, it is desirable to provide an automatic blood pressure measuring device including apparatus for preventing substantial buildup of dust, dirt, and other debris in the pneumatic system thereof.
Further, due to the resistance to gas of the pneumatic system, minor variations exist in the target pressure to which the data processor attempts to deflate the cuff and the actual pressure that is reached in the steady state. The effect of this resistance, and the difference between the target and actual pressures, is increased as dust, dirt, and other debris is accumulated in the pneumatic system.
Some systems have been developed with software that to provides a compensated target pressure, less than the target pressure by an offset value, so that the pressure is reduced to the compensated target pressure. As the system reaches equilibrium, and the pressure in the pneumatic system rises, the pressure in the pneumatic system approaches the target pressure so that the actual steady state pressure in the pneumatic system is substantially equal to the target pressure. However, these systems do not provide adequate compensation for extremely high resistances, which resistance cause the measurement to lose accuracy and may be dangerous to the patient. Therefore, it is desirable to provide method and apparatus for use with an automatic blood pressure measuring device that will eliminate loss of accuracy of the measurement and danger to the patient caused by extremely high resistances in the pneumatic system.